Observations and modelling of the Martian water vapor budget for 1988-1989.
AdvisorHunten, Donald M.
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PublisherThe University of Arizona.
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AbstractDuring 1988-89, the 1.5 m telescope on Mt. Bigelow, Arizona, combined with the Lunar and Planetary Laboratory echelle spectrograph, recorded 20 spectral CCD images of Mars during early spring, mid- and late summer, and autumnal equinox in its southern hemisphere. These images contained absorption features which permitted latitudinally resolved measurements of water vapor column abundance in the martian atmosphere on these four occasions, corresponding to the areocentric longitudes (L(s)) 208, 320, 340, and 360°. This dissertation describes the acquisition, analysis, and modeling of this data set. Photochemical models at different latitudes predicted ozone column abundance at L(s) = 208° when initialized by the observed water vapor abundances. Matching simultaneous ozone abundances, also measured from the ground, required eddy diffusivities at altitudes between 5 and 15 km that were at least two orders of magnitude lower than the values greater than 10⁸ cm² sec⁻¹ assumed above 30 km altitude, especially at south polar latitudes. Legendre polynomials and interpolating parabolas described the observed spatial and temporal behavior of the martian water vapor for L(s) = 320, 340, and 360°. Integrating the fits with latitude derived visible disk and globally averaged abundances as a function of time. A budget based on these abundances suggested the southern hemisphere subsurface to be a source, and therefore a reservoir, of water vapor during this season. The large magnitudes and signs of effective meridional diffusivities for the data implied the water vapor's disappearance to be more likely due to condensation and adsorption into local sinks than to atmospheric transport. When compared with Viking water vapor data, the Catalina abundances hinted that dust was a mechanism for shielding water vapor from ground-based observation and that northward transport was more efficient during a dusty southern spring and summer than during a dustless one. Finally, a one-dimensional analytical meridional diffusive model and a two-dimensional diabatic circulation water transport model confirmed the idea of a southern hemisphere surface source and sink for the Catalina water vapor, and more efficient northward water transport during dusty southern spring and summer. Moreover, both transport models suggested that the large amount of water seen from the ground during 1969 was not sublimed from a south polar residual cap of water ice.
Degree ProgramPlanetary Sciences